Shrouded combustion liner

ABSTRACT

A gas turbine combustion chamber having an outer casing and a concentrically mounted inner liner. The inner liner is formed with annular rows of spaced louvers for admitting cooling air and annular rows of spaced primary air holes. A shroud is circumscribed about the inner liner and spaced there from. Annular rows of spaced cooling air holes are formed in the shroud and direct jets of cooling air to hot spots or hot highly stressed areas between the louvers. The presence of the shroud makes it possible to increase the opening of the louvers for increasing the thickness of a cooling air film. The shroud also is formed with primary air holes which are slightly larger than and in approximate register with the primary air holes in the inner liner.

Q United States Patent 1191 1111 3,777,484 Dibelius et al. Dec. .11,1973 SHROUDED COMBUSTION LINER 1 [75] Inventors: Norman R. Dibelius,Ballston Spa; 5 g 'l ifg g Garden Richard B. Schiefer, Schenectady, bothof N.Y.

[73] Assignee: General Electric Company; [57] ABSTRACT Schenectady, NY.A gas turbme combustion chamber having an outer [22] F'led: 1971 casingand a concentrically mounted inner liner. The 211 App}. 20 021 innerliner is formed with annular rows of spaced louvers for admittingcooling air and annular rows of spaced primary air holes. A shroud iscircumscribed [52] US. Cl. 60/39.65, 60/139166 about the inner liner andspaced there from Annular [51] III It. Cl. F02C 1/00 rows of spacedcooling air holes are formed in the [58] FIG! of Search 60/39.65, 39.66Shroud and direct jets of cooling air to h spots or hot highly stressedareas between the louvers. The pres- [56] References cued ence of theshroud makes it possible to increase the UNITED STATES ENTS opening ofthe louvers for increasing the thickness of 3,016,703 1/1962 Lorett60/39.65 a ling air film. The shroud also is formed with pri- 3,570,24l3/1971 Alexander.. (SO/39.65 UX mary air holes which are slightly largerthan and in ap 3,169,3 5/1965 ussey 60/39-65 UX proximate register withthe primary air holes in the inner liner FOREIGN PATENTS OR APPLICATIONS3 Cl 5 D F 537,213 2/1957 Canada 60/39.65 guns T r a La .,,,,X & a e Mif? f SHROUDED COMBUSTION LINER BACKGROUND OF THE INVENTION Thisinvention relates, in general, to a combustion chamber for a gasturbine, and in particular, this invention pertains to a shroud coverfor a combustion chamber liner. I

In a gas turbine, one of the more vulnerable parts, in terms of earlyreplacement required, is the combustion liner of the combustion chamber.The combustion liner is subjected to extreme heating conditions andtemperature stresses due to its proximity to the luminous flame and hotgases supporting the combustion process. Therefore, it is important tomaximize the effect of cooling air adjacent the combustion liner inorder to prolong the useful life of the combustion liner.

Air delivered to the combustion chamber has two functions. One function,already mentioned, is to provide some cooling of the liner while theother function is to provide the precise amount of primary air necessaryto support optimum combustion conditions. Too little primary air mayresult in incomplete combustion and smoking; and, too much air mayresult in flame instability or a tendency to blow out.

SUMMARY The combustion chamber of a gas turbine includes an outer casingand a concentrically mounted inner liner havinga number of annular rowsof spaced louvers. The inner liner is also provided with a number ofannular rows of spaced primary air holes. A shroud is circumscribedabout and spaced from the inner liner and supported thereon; and theshroud is formed with a plurality of annular rows of spaced coolingholes. The shroud cooling holes are accurately positioned to provide jetimpingement cooling air to the hot, highly stressed, areas or hot spotsbetween the louvers for the purpose of relieving the temperaturegradient and reducing thermal stresses. The presence of the shroud reduces the pressure drop across the louvers with a correspondingreduction in the velocity of the air through the louvers. This makes itpossible to increase the opening of the louver which results in anincrease in the thickness of the cooling air film and improves thecooling. There are also annular rows of spaced primary air holes in theshroud slightly larger than and in approximate register with the primaryair holes in the inner liner. The size of the primary air holes in theshroud must be 1.25 to 1.70 times larger in area than the air holes inthe louvered liner in order not to upset the air flow pattern throughthe primary air holes in the liner.

It is therefore one object of the present invention to provide animproved combustion chamber which will increase the effectiveness of thecooling air flow adjacent the wall of the combustion liner.

Another object of the present invention is to provide an improvedcombustion chamber which will support optimum combustion conditionswhile maximizing the effectiveness of the cooling air flow.

Other objects and advantages will become apparent from the followingdescription of one embodiment of the invention, and the novel featureswill be particularly pointed out hereinafter in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cut away,elevation side view of a part of a gas turbine combustion chamber inwhich the present invention is employed with arrows indicating theapproximate flow of air.

FIG. 2 is a top view of a section of the inner liner and a shroudapplied thereto according to the present in vention.

FIG. 3 is a diagramatic representation of the cooling air flow through alouver in the combustion chamber inner liner as found in the prior art.

FIG. 4 is an enlarged side view section of the liner and shroudaccording to the present invention with arrows indicating theapproximate flow of air.

FIG. 5 is a graph illustrating the rate of temperature rise as thecooling air passes through the louvers in both a shrouded and unshroudedliner.

DESCRIPTION OF THE PREFERRED EMBODIMENT A portion of a gas turbinecombustion chamber 11 is shown in FIGS. 1 and 2, and 4 including anouter casing 13 and a concentric inner liner 1.5, the latter defining acombustion zone 17. A fuel supply pipe 19 enters the forward end of theouter casing and communicates with a fuel nozzle 21 at the forward endof the combustion zone.

The inner liner of the combustion chamber includes a number of annularrows of spaced louvers 25 which direct the flow of cooling air so thatit forms a film of cooling air immediately adjacent the interior wall ofthe inner liner in a manner which will be later described.

A number of annular rows of spaced primary or combustion air holes 27are provided in the inner lining for delivering air to the combustionzone.

A shroud 31 is concentrically mounted around the inner lining and spacedtherefrom and includes a plurality of annular rows of spacedcoolingholes 35 which provide cooling air into the space between theshroud and the liner and from there to be directed by the louvers intothe combustion chamber. The holes 35 are also arranged so that coolingair is directed in jets toward hot spots 37 immediately preceeding andin between louvers 25.

There are also provided, in the shroud, a number of annular rows ofspaced primary or combustion air holes 39 which are substantially inregister with the primary air holes 27 in the inner liner but are largeras shown in FIG. 4. The primary holes in the shroud are about 1.25 to1.70 times larger in area than the primary air holes in the liner,dependent upon the annular spacing between the shroud and the liner.

OPERATION In FIG. 3, there is shown an enlarged view of an unshroudedlouver with a supply of cooling air as disclosed in the prior art. Heatfrom a. luminous flame (not shown) is transferred to the liner wallpredominently by radiation from the combustion flame and the liner wallis cooled primarily by forced convection to the cooling air which flowsthrough the louvers and forms a cooling film on the inside surface ofthe liner.

As shown in FIG. 3, zone 1, cooling air is heated by mixing with the hotair film from upstream of the louver opening and by convection from thehot liner wall. Also the difference in temperature between the coolingair and metal is great in zone 1. Note that the mixing zone in thisprior art representation exhibits a high degree of mixing due to thehigh velocity of the cooling air through the unshrouded louver shearingthe hot air stream. As shown by the broken line in FIG. 5, zone 1 therate of temperature rise is rapid as contrasted with the rate oftemperature rise in zone 2. In zone 2 the temperature of the cooling airis closer to that of the liner metal and heating becomes a function ofthe liner metal primarily and so the rate of temperature rise isdiminished.

In order to improve the effectiveness of the cooling air withoutincreasing the quantity of cooling air, the effect of mixing the coolingair with the hot film must be reduced. This can be done in two ways. Thefirst is to reduce the difference in velocity between the cooling airand the hot air film, thus reducing the shear which results in thereduction of the mixing of the two gas streams and, secondly, byincreasing the height of the louver as shown in FIG. 4 to make thecooling air film thicker. In order to accomplish this without increasingthe quantity of cooling air, the pressure drop across the louvers mustbe reduced without reducing the pressure drop across the primary orcombustion air holes. This can be done by surrounding the louvered linerwith the perforated outer shroud as heretofore described. In addition,the perforations or cooling air holes can be located above the hotstressed areas 37 between louvers thus taking advantage of jet coolingof the hottest area. The effect of placing a shroud on the combinationliner is shown in FIG. 5, solid line, where the temperature rise in theshrouded liner is less than that of the unshrouded liner in zone 1, aswell as the end temperature conditions in zone 2.

If the combustion air holes in the shroud are too much smaller thanthose in the liner the combustion air jet will entrain air from thespace between the shroud and the liner and if they are too much largerair will spill into the space between the shroud and liner, but if theratio of the combustion air hole areas is in the approximate range from1.25 to l to 1.70 to l shroud to liner, the jet will neither spill overor entrain extra air and a tube connecting inner liner and outer shroudaround the combustion air holes is not necessary.

Thus the invention will improve liner cooling with a reduction of linertemperature and hot spots which would increase the strength of thematerial in the area where the low cycle thermal stress fatigue cracksoccur and therefore the liner life should be increased many times overthat for an unshrouded liner.

While there is shown what is considered to be the preferred embodimentof the invention, it is of course understood that various othermodifications may be made therein and it is intended to cover in theappended claims all such modifications as fall within the true spiritand scope of the invention. I

What is claimed is:

1. In a gas turbine combustion chamber of the type including an outercasing having a fuel nozzle disposed therein communicating with an innerliner concentrically mounted within the outer casing, said inner linerbeing formed with annular rows of spaced louver openings and annularrows of spaced primary air holes along the length thereof, and furtherincluding:

a shroud surrounding the liner and spaced therefrom including aplurality of annular rows of spaced cooling air holes along the lengthof the shroud to overlie the areas between the annular rows of spacedlouver openings;

the shroud further including a plurality of annular rows of spacedprimary air holes substantially in register with and larger than theprimary air holes in the liner.

2. The combustion chamber recited in claim 1 wherein the cooling airholes are disposed to overlay hot spots on the inner liner between thelouver openings.

3. The combustion chamber as recited in claim 1 wherein the primary airholes in the shroud are in the range 1.25 to 1.7 times larger in areathan the primary air holes in the liner, the exact value dependent uponthe spacing between the shroud and the liner.

1. In a gas turbine combustion chamber of the type including an outercasing having a fuel nozzle disposed therein communicating with an innerliner concentrically mounted within the outer casing, said inner linerbeing formed with annular rows of spaced louver openings and annularrows of spaced primary air holes along the length thereof, and furtherincluding: a shroud surrounding the liner and spaced therefrom includinga plurality of annular rows of spaced cooling air holes along the lengthof the shroud to overlie the areas between the annular rows of spacedlouver openings; the shroud further including a plurality of annularrows of spaced primary air holes substantially in register with andlarger than the primary air holes in the liner.
 2. The combustionchamber recited in claim 1 wherein the cooling air holes are disposed tooverlay hot spots on the inner liner between the louver openings.
 3. Thecombustion chamber as recited in claim 1 wherein the primary air holesin the shroud are in the range 1.25 to 1.7 times larger in area than theprimary air holes in the liner, the exact value dependent upon thespacing between the shroud and the liner.